A frequent source of operating problems in refining and hydrocarbon processing units is the formation of deposits throughout those units resulting in an increase in pressure drop, decrease in efficiency, increase in energy consumption, loss of operating time, and other well-known difficulties. These deposits include salts of ammonia, inorganic contaminants that enter the process in the feed, and deposits that develop as by-products from corrosion of the processing unit including metal sulfides, metal oxides, metal hydroxides, and other metal salts. These deposits alone or in combination with other hydrocarbon polymers and decomposition products often form deposits that are difficult to remove from the internals of the processing units.
During the processing of hydrocarbon liquids, such as crude oil, under the elevated temperature conditions of a refinery, small amounts of water emulsified or otherwise entrained in the hydrocarbon will first vaporize and then later condense on the metallic surfaces of the equipment overhead of high temperature units, such as distillation columns. This water contains acidic elements, predominantly hydrochloric acid (HCl), which will corrode the surfaces of the overhead equipment at locations where condensation occurs.
In an attempt to minimize this corrosion, hydrocarbon processors will add chemical compounds to the hydrocarbon prior to elevated temperature processing for the purpose of neutralizing the acid, e.g., HCl. The compound most frequently employed is ammonia. The ammonia will neutralize the HCl by forming ammonium chloride.
The neutralization of HCl by ammonia mitigates against the problems of corrosion but the formation of ammonium chloride causes others. The ammonium chloride, which is vaporized during elevated temperature processing, is sublimed onto the surfaces of the overhead equipment. Sublimation, as herein defined, is intended to mean that the ammonium chloride passes directly from the vapor state to its solid crystaline form, bypassing its liquid phase. Crystaline ammonium chloride builds up on these surfaces resulting in the operational problems previously discussed.
It is an object of the present invention to inhibit the growth of ammonium chloride deposits on the surfaces of the overhead equipment in a hydrocarbon refinery. The aforementioned problems are overcome by the present invention which discloses a method for the complete removal and/or prevention of the formation of deposits of ammonium chloride.